1. Field of the Invention
The present invention relates to a method for manufacturing a sputtering target, a method for forming an oxide film, and a transistor.
2. Description of the Related Art
Transistors used for most flat panel displays typified by a liquid crystal display device or a light-emitting display device are formed using a silicon semiconductor such as amorphous silicon, single crystal silicon, or polycrystalline silicon provided over a glass substrate. Further, such a transistor employing such a silicon semiconductor is used in integrated circuits (ICs) and the like.
In recent years, attention has been drawn to a technique in which, instead of a silicon semiconductor, a metal oxide exhibiting semiconductor characteristics is used in transistors. Note that in this specification, a metal oxide exhibiting semiconductor characteristics is referred to as an oxide semiconductor.
For example, InGaO3(ZnO)m (m: a natural number) having a homologous phase is known as an oxide semiconductor (see Non-Patent Documents 1 and 2).
In addition, Patent Document 1 discloses a transparent thin film field-effect transistor including a homologous compound InMO3(ZnO)m (M represents In, Fe, Ga, or Al, and m is an integer greater than or equal to 1 and less than 50).